Double interpolation method and apparatus for measuring time intervals



FRADY, JR 2,665,411

W. E. DOUBLE INTERPOLATION METHOD AND APPARATUS FOR MEASURING TIME INTERVALS Jan. 5, 1954 Filed March 15, 1951 5 Sheets-Sheet 5 Fwi' 2 CIRCUlT FROM 0 comcmsuc:

i CIRCLHT GATE PULSE!) T C osuLLA'roR r FIXED PULSE DELAY SHAPER FC j I 1 {1 43 '44 v5 u u ()R GATE R CIRCUIT C Q I CIRCUIT FRACTION COUNTER P P h V 2 2 A l 3 l 49 a naaanaamaa l la. A Lj INVENTOR. WILLIAM Ea FRAmgJR,

Jan. 5, 1954 w FRADY JR 2,565,411

DOUBLE INTERPdLATION METHbD AND APPARATUS FOR MEASURING TIME INTERVALS 5 Sheets-Sheet 4 Filed March 15, 1951 DECODER la a w "OR; QT-M P CIRCUIT 2 PULSEB UNIT 855351432 050mm ,22 i 13 PULSE PULSE SHAPER 5 SHAPER CA CQINCIDENCE \b cmcuuT 23,

O J C-ATE I 63 c 25 r {I 64 f c GATE CATE v GATE F 0Q- We GATE GATE c e FIXED "0R" "0R" DELAY CIRCUlT c|Rcu|T 7\ j x i e GATE cmcun' J r ,24 12 FIRST SECONB UNT FRACTION FRACTION coum'm COUNTER COUNTER E j INVENTOR.

WILLIAM EOFRADYMR.

Patented Jan. 5, 1954 N? F F H C i DOUBLE INTERPOLATIQN METHOD/AND APPARATUS FOR MEASURING TIME IN TERVALS.

William E; Frad'y, J r'.',

to poration of Delaware- Los Angeles; (lalifa-assig non- Hughes ToolCompany, Houston, Tex., a cor- Application March 15, 1951', Serial No; 215,69'0

(Cl. 324.-68)r MIClaims. i

The present invention relates to a double interpolation method and apparatus for measuring time intervals and more particularly to a double interpolation method and apparatus for measuringitime intervals wherein a single signal genera-- tor, is utilized to produce bothinterpolation signals.

In copending. United States patent application SerialNo. 215,691 for Method and-Apparatus for Measuring Time Intervals, byD'. Burbeck, filed March 15, 1951; there is set" fortha double interpolation method and apparatus for measuring the time interval between a pair of spaced signals. According to the method of this application, a continuously running signal generator is utilized-to measure the number of unit time intervals in the time interval to be measured; and a pair of vernier signal generators are utilized to -measure the fractional time intervals remaining at each endof the time interval to be measured. The periods of the threegenerators are each difierent from, butclose to, the others.

One of the vernier signal generators is actuated by the'first signal of the pair of signals to produce a first series of vernier signals, while the other vernier signal'generator is actuatedby the second signal of the pair of signals to produce a second series of vernier signals. Measurement of each of the fractional time intervals is made by counting the numbers of vernier signals of each V series occurring during the time intervals between the first signal of the series and coincidence between a signal of the series and asignal from the continuously running generator;

Since the fractional measurement will, therefore, be dependent upon the time delay in actuating the vernier signal generator, it is clear that any difierence between the timedelays in actuating the vernier signal generators will introduce a direct error in themeasurement of the total fractional time interval. Accordingly; great care mustbe exercised incontrollingthe time delay in reach-of the vernier generators; and, in ma-in-f. tain-ing an equal delay in each vernier generator,-

Furthermore, since, thevernier signal generators are pulsed generators, they aresusceptible to frequency driftwhich introduces -a further error into the measurements. By utilizing two: vernier signal generators, the possibility of error inthe, final result, due to frequency. drift .is twofold.- Thus, if it is assumedthat.eachgenerator has a maximum frequency drift in either direction of a predetermined percentage, the error introduced into the total measurement by frequency drift Lil) may, havea valuejproportional to twice the predetermined percentage:

The present invention discloses a method" and;

apparatus for measuring: the time. interval betweenapair: of spaced? signals wherein a single.

vernier signal generatoris-utilized-to measure both fractionalc time intervals. By utilizing the single vernier signal generator; thepossibility of error due toi-frequency drift is reduced .to-a value directly proportional to the predetermined percentage. Furthennore; since-a singlexverniersignal generator: is used-:for both' fractional time intervals, the time delay in actuating the generator is the, same for each: of; the pair of input signals, and no error: is" introducedinto. the measurements because ofrthisrdelay. Stated-differently; any-:error: introduced intov the first fractional timeintervalgmeasurement by the time delay will be compensated for by an equal'andj opposite error in-troducedinto' the second fractional time interval measurement by: this delay. Accordingly; the: use; of a single vernier" signal generator.- not only: eliminates: the necessity of accuratetimedelay control of a pair of'generators; but also eliminates the necessity of employingza fixed timerdelay; since any delay will bequires a minimum .number' of components. andhas.a-maximumaccuracw Another object is to provide :adouble interpolation time interval measuring method and ap- V paratus which employsea single vernier signal generator for performing both interpolations.

Afurther. obiectpfzthe inventionis to provide a double interpolation" time," interval measuring method: and apparatus which'employs a single vernier signal? generator having a period 1 either greater or less-than that of the continuously runhing-signal generator;

Still anotherobjectds =to-provide a double interpo tionztime interval:measuring method and apparatus:- whrch': employs: a. singlezverier signal:

.erator and which eliminates any ambiguity as he measurement of the unit time interval. he novel features which are believed to be ,racteristic of the invention, both as to its anization and method of operation, together h further objects and advantages thereof will better understood from the following descrip- 1 con idered in connection with the accomiy ng drawings in which several embodiments the invention are illustrated by way of exples. It is to be expressly understood, howr, that the drawings are for the purpose of .stration and description only, and are not inded as a definition of the limitsof the invenig. 1 is a composite diagram of waveforms for alaining the basic principle of the present inition.

Pig. 2 is a block diagram of one embodiment the invention.

F'ig. 31s a composite diagram of waveforms :urring at various points in the circuit of Fig. 4 is a block diagram of a modification of a circuit of Fig. 1, in which a single up-down LCtlOIl. counter is employed.

Fig. 5 is a block diagram of a modification of e fraction counting section of the circuit of g. 1, wherein a single conventional fraction unter is employed.

Fig. 6 is a composite diagram of waveforms curring at various points in the circuit of Fig. '7 is a block diagram of non-ambiguous rcuit according to the present invention.

Fig. 8 is a composite diagram of waveforms :curring at various points in the circuit of Fig. '7.

Fig. 9 is a block diagram of a modification of i8 circuit of Fig. 7i and Fig. 10 is a composite diagram of waveforms :curring at various points in the circuit of Fig. 9.

Referring now to the drawings, there is shown Fig. l a composite diagram of waveforms r illustrating and explaining the basic prinple of the present invention. In Fig. 1, incom- Lg pulses P1 and P2 are separated by a time in- -rval At to be measured. According to the iuble interpolation system, time interval At is Lvided into three components, a unit time in- :rval T1 and a pair of fractional time intervals 2 and T3. Unit interval T1 is determined by 1e number of unit signals or pulses occurring uring the time interval At. Fractional time iterval T2 is the time interval between pulse P1 nd the first unit pulse occurring during interval t. Fractional time interval T3 is the time inzrval between pulse P2 and the last unit pulse ccurring during interval At.

A vernier frequency signal generator is used 3 measure intervals T2 and T3, the period of ."le vernier signal generator being related to the eriod of the unit signal generator in accordance rith the relationship n+1 or 11,-1

where n is an integer. Thus, the number of 'ernier signals or pulses occurring during the nterval between pulse P1 and a first coincidence )etween a unit pulse and a vernier pulse is epresentative of interval T2, if the vernier sigial generator is initially triggered by pulse Pl. Similarly, if the vernier signal generator is firially triggered by pulse P2, the number of vernier signals or pulses occurring during the interval 4 between pulse P2 and a second coincidence between a unit pulse and a vernier pulse is representative of interval T3.

Referring again to Fig. 1, consideration is given first to the case of the low frequency vernier, that is the period of the vernier'signal generator being related to the period of the unit signal generator in accordance with the relationship In the illustrated example, the period of the unit signal generator is represented as being equivalent to inch, and n is 8. Therefore, the

period of the vernier "signal generator is represented as being equivalent to inch. It is understood, of course, that the selected periods and value of n are merely illustrative and that any other values may be chosen.

As shown in Fig. 1, the number of vernier pulses t2 occurring between pulse P1 and the first coincidence is directly proportional to interval T2, and, in termsof unit intervals, is equal to the pulse count t2 divided by n. On the other hand, the number of vernier pulses is occurring between the first coincidence and the nth vernier pulse is directly proportional to interval T5, where T2 plus T5 equals one unit time interval. Thus, it is seenthat interval T2 may be measured by counting either the number of vernier pulses t2 between pulse P1 and the first coincidence, or the number of vernier pulses t5 occurring between the first coincidence and the nth vernier pulse. In the latter case, the measurement of interval T2,'in terms of unit intervals, is equal to 1 minus the recorded count t5 divided by n.

Interval T3 may be measured in a manner similar to that outlined above. It is to be noted, however, that in measuring interval T3, the number of vernier pulses t4 occurring between pulse P2 and the second coincidence is directly proportional to interval T4. Accordingly, if the count recorded is between the incoming pulse and coincidence in each instance, the total fractional count, in terms of unit intervals, is 1 plus the difference between the counts divided by n, that the results obtained are opposite to those obtained in the case of the low frequency vernier signal generator. Thus, as indicated in Fig. 1, the number of vernier pulses is between pulse P1 and the first coincidence is directly proportional to interval T5, while the number of pulses s occurring between pulse P2 and the second coincidence isdirectly proportional to interval T3.

Accordingly, if the count recorded is between the incoming pulse and concidence in each instance, the total fraction count, in terms of unit intervals, is 1 plus the diiference between the counts divided by n, that is Itwisthus;seenthatebyspropengatinaoi the-trace tion counter;interralseTzandTrmar'be-measured y: arsinelecverni r ienalrgeneratorg.

Referring :noww o: Eis; 2; thereziswshewn one form; of: double interpolation: system-.1 according; to the present invention which employsza-single; rni r; r du n ya scillaton and: repair-:- .ira io al omter.s;;.. Fig.1 2',- v. heumi ;m.e surine; sot npf heisystemz omprise r ontinuou ly. um le-un t pulse-oscillaton-l-l a oupledto a.:.unit n r 2; hr uehap ls shaperrl 53131: agate M: he output; of DQ115532 haper: 3.- s; appli d to oneinputt m na of a: coin idence ircuit! .5: Ae ur anot sh wnrof.i comi aen lsez i ndemisconnected; tothe input terminal of a decoder; l 6 through conductor 1 l, the output 1 terminals; oidecorder--- It being, connected; respectivelrlyto the input-.termina1s ,.of an orcircuit 1 8.;.'De-- corder l Gris any suitableci-rcuitzfor dividing-jpulses" P1 and, P2 into.- ;two separate, lines, I one suitable decoder. being; illustrated:- ineF-ig. 2 of ,copending; United States, patent. application- Serialv No. 215,692 for Method;andlApparatus;for 1ltlleasuring-Time Intervals? by H-rBrooks-and D. Bur. beckfiled March 15, 1951'.

The-output-terminal or for? circuit ta is-connected to the input end 01 the fraction measuring sectionoi the system.- "lhissectionyinoludes a pulsed oscillator IQ for initiatingoscillations of oscillator I9, the output of oscillator i9 =being applied to a first-fractional: counterZ-i through'a pulse'shaper 22- and: a; gate 23; The output; of oscillator. l9also is applied to-a second fraction counter- 24 through; pulse shaper 22 and; a gate 25; Theoutput terminal of pulse shaperzr22' is connected to the other "input terminal of coincidence circuitiIE,

The-outputterminals.:.ofdecoder I6" also. are coupled to the openingandi closing control .=ter,- minals, respectively, of gate l4, SQwthah gate 14 is opened by pulse P1 and closed by pulse P2. The opening control terminalspf gates 23 and 25 also are connected to the output terminals, respectively, of decoder 16, so that gate 23 isopened by pulse P1,.andgate 25..is openedbypuls'e P2. The output terminalof coincidence circuit l5, is connected'to the, closing. control. terminals of gates23 and 25. sov that closingof gates .23 and 25 occurs ,vwhenevera signal appears in the outputof coincidence. circuit i 5.-

Coincidence. circuit; llmay be. anysuitable cir.- cuitcapable of producing an output pulse whene ever the. pulses a on itsinput terminals coincide. One, suitable circuitzis that. illustrated-in Figs; l0. -l.18. on page 3810f vol. 19-ofthe M; I. T. Radiation Laboratory Series,- published in 19.49 by Mo- (irate-Hill BookCompany, -wh-ichis-hereby: made a part of this application.

In operation, referring;to 3,,theptimeintervalto be measured'is the 1 interval "At between pulses. E1 and P2 asthey occur at pointa, .in the systemof Fig. 2. The intervalAt-is divided .into threeL components,- a: unit time interval T1-, a first fractional time interval ,Tz betweenapulse :Pl and the'initial pulseaa-ppearing a-t poi nt e during the timeinterval to be-measured; and a fractional timeainterval Tzbetween the' final pulse appearing- -at pointb-duringthektime interval to be measured-and pulse P2. Trisrmeasured by unit-counter l2; and fraction time intervals-T2 and'Ta' are indicated by trace tionalicounters 2! and 25, respectively.

Oscillator H is continuouslyirunning and'pro: ducesa first series of uniformlyjspaced pulsesat The unit time interval counter l2. Gate I t-remains open until the appearance of pulse P2 at the output of decoder I6. Thus, the total number of pulses i'r appearing at point-wand counted by unit counterl2 represents, in terms of the period of oscillator I l-, theunit time interval T1.

The appearance of pulse-P1 at the output of decoder I 6 triggers oscillator I 9 and initiates a second series of uniformly spaced pulses'at point c, the output of pulse shaper 22'; Pulse Pr also opens gate 213 'so'th'at the-secondyseries-of pulses appearsatpoint e; theinput of fraction-counter 2!; Gate 23 remains open-until coincidence occursbetween -apulse'of" the first series at pointvb' and a pulse'ofjthe secondseries-at point '0'; At this coincidence; a signalappears-in the output of coincidence circuit l5 and closes gate-2t;- A ccordingly the-number of pulses t2 appearing, at point e and counted by first fraction counter-21 are representative ofthe fractionaltimeinterval T2.

quencies of. oscillators ll and'lflis in accordancewith the relationship where-n is an integer, the count t2 produced'in the fraction counter 2| will be directly-proportional to the fractionaltime interval Ta; On-the other hand, if the frequencyof oscillator- II is lower than the frequency of oscillator I9, that is the ratio of the frequencieszof oscillators II and I9 is in accordance with the relationship where n is an integer, the count t2 recorded by fraction counter 21 is proportional to 1T2.

Although the output of pulse shaper '22 also is appliedto-gate -25, no pulses appear at-point f the input to fraction counter 24, since gate 25 remains closed until the" appearance of pulse P2. At the appearance of pulse P2 at the output of decoder I6;- oscillator' i9 is again triggered-and produces a-third series of pulses at point-c: With gate 25 opened by pulse P2, this third-series of pulses appears at point f,"the" input'of fraction counter 241' Gate'ZB'remainsbpen until a second coincidence between a pulse at point D and a pulse at' pointc; at-;which time a pulse appears at. the output-end; of" coincidence circuit; t5? to close gate-25; Accordingly, the seriesnof pulses tajape pearing at point f and counted by fraction counter 2 is representative of the. fractionaltime intervalTs.

The relationship. betweenthej count of fraction counter 24 1 and interval ,T: is the -reverse. of that between the. count of counter, 2 l.,and, interval; T2.

Stated differently, .ifthefrequencypi oscillator I I is higherthan that of'oscill'ator t9, thev count is of fraction counter 24 is proportionalto 1 T3, while if the freouency of oscillator l l;islower than that of oscillator l9, the count t3 of fraction in that of oscillator H, as indicated in Fig. 3, a total fractional count, in terms of unit inters or counts, is equal to oscillator |9 has a higher frequency, the total LCtiOIlSl count, in terms of unit intervals, is ual to either case, in obtaining the total count of terval At, it becomes necessary to add one count the unit count 151 to obtain the exact result. )wever, referring to Fig. 3, it can be seen that e unit count recorded in counter |2 is actually [8 greater than the number of unit time inter- ,ls between pulses P1 and P2. Accordingly, the MM of counter |2 inherently includes the extra iit count. Referring again to Fig. 3, it can be seen that :cillator it was chosen as having a time delay ual to one period of its oscillations. However, i pointed out above, the use of a single vernier icillator permits the time delay of oscillator to a chosen as any desired value. This result folws from the fact that the total fractional count I. any measurement is proportional to the difarence between the two fractional counts, that i either ta-tz or tz-ts. Thus, if the time dety were either shorter or longer, the gain or loss 1 count t2 would be compensated for by the equal ain or loss in count t3, the difference remainig constant.

The total count of interval At, in terms of unit atervals, is, therefore,

iy-ta 1+ n or the high frequency Vernier. The necessary iddition and subtraction may be performed in my suitable manner, such as visually or elec- .ronically.

Referring now to Fig. 4, there is shown a modiication of the system of Fig. 2, wherein a single :ounter and a single gate are utilized for countng the fractional time intervals T2 and T3. The mit counting section of the system of Fig. 4, :omprising oscillator shaper l3, gate l4 and counter I2, is identical with and operates in the same manner as its counterpart in Fig. 2. Similarly the fraction pulse generator, comprising for circuit I8, oscillator l3 and shaper 22, corresponds to the generator of Fig. 2. Coincidence circuit l5, decoder l6 and input conductor H are connected in the same manner as the corresponding elements of Fig. 2.

In Fig. 4, a single fraction counter 3| is employed for counting intervals T2 and T3, counter 3| being capable of counting either up or down. Although any up-down counter is contemplated by the present invention, one suitable form is that shown in Figs. 4 and 5 on pages 963 and 964 of Electrical Engineering, November 1949, in an article entitled "The Binary Quantizer by Kay Barney. In this counter, up or forward counting is produced by an incoming positive pulse, while down or backward counting is produced by an incoming negative pulse. Accordingly, it is merely necessary to invert one of pulses P1 and P2 before applying it to counter 3|. This is indicated schematically in Fig. 4 by an inverter 32 in the line between decoder H5 and the down control of counter 3|. Obviously, many conventional circuits will perform the function of inverter 32, one such circuit being a common amplifier.

Coupled between pulse shaper 22 and counter 3| is a gate 33 for controlling the transmission of the vernier pulse series to counter 3|. The opening control terminal of gate 33 is connected to the output terminal of or circuit |B, so thatgate 33 opens each time either pulse P1 or pulse P2 appears at the output of or circuit IS. The closing control terminal of gate 33 is connected to the output terminal of coincidence circuit l5, so that gate 33 closes at each coincidence.

In operation, the unit count 121 is produced in the same manner as in the circuit of Fig. 2. The fraction counts are produced in counter 3| in the same manner as in counters 2| and 24 of Fig. 2. Thus, if oscillator I9 has the lower irequency, counter 3| is arranged as shown in Fig. 4, and the total count of counter 3| is proportional to t2t3. On the other hand, if oscillator I9 has the higher frequency, pulse P1 is applied to inverter 32, and the count of counter 3| is proportional to t3-tz.

In each of the embodiments thus far described, it is necessary to perform a subtraction operation in order to obtain the fractional count, this subtraction being performed externally, as in Fig. 2, or being performed by a particular type of counter, as in Fig. 4. The system of Fig. 5 includes a single fractional counter and means for counting intervals T2 and T3 directly on this single counter by simple addition. In the system of Fig. 5, only a lower frequency Vernier oscillator may be used, that is the ratio of the frequencies of the oscillators is in accordance with the relationship Where n is an integer.

Referring now to Fig. 5, only the fraction measuring section of the system is illustrated, since the unit measuring section to be employed is identical with that of Fig. 2 and Fig. 4. Incoming pulse P1 and P2 are applied to the input terminals of or circuit I8, the output terminal of circuit l8 being connected to the input terminal of pulsed oscillator |9. Circuit I8, oscillator l9 and pulse shaper 22 are identical with, and per form the same function as their counterparts in Figs. 2 and 4, namely the production of two series of pulses at the output of shaper 22. The output of shaper 22 is applied to a counter 4| through a gate 43. I

Gate 43 has its opening control terminalconnected to the output terminal of or circuit 44, and its closing control terminal connected to the output terminal of or circuit 45. Pulse P1 is applied to one input terminal of circuit 44, the other input terminal of circuit 44 being connected to the output terminal of a gate 45. Pulse P2 is applied to the opening control terminal of a gate 49 which has its output terminal connected to its closing control terminal and, through a fixed delay circuit 41, to one input terminal of circuit 45. The other input terminal of circuit 45 is connected to the output terminal of a gate 48. Pulses P1 and P2 are applied to the opening control terminals of gates 43 and 46, respectively, the closing control terminals of gates 46 and 48 being connected to their respective output termi- 'nals. :Theoutput of the is again triggered and opened, and pulse a essgni coincidencecircuit, not shown, is applied to the input-terminalof-each of gates 46 and 48.

In operation, referring-to Fig. 6, 'pulses P1 and P2 are separated by atime interval At, and-pulses 49, the output of the un-it oscillator and-the unit pulse shaper, are again-used to measurethe unit time interval T1. Oscillator i9 is'initiallytriglgered by pulse P1 toproduce a first series ofpulses atv point a, and finally triggered by pulse Pz to produce a second series of pulses at -poi nt fa. Pulse P1 is also applied togate 43' through circ'uit 44, and the first series ofpulses-will'appear'at point D, the inputto counter 4|. In addition, pulse P1 is applied to gate l to' open gatedt. Upon coincidencebetween a pulse from=shaper 22 and a unit pulse, a signal "appears at the output of the coincidence circuit and'is' appliecl'to gates 46 and 33. With gate'48 open,this signal is applied through circuit 5 to close gate l3. -Accordingly, the totalnumber of pulses tz'of the first series appearing at point D and counted by counter 43! is representative ofthe'interval T2. If the frequency ofoscillator l9 is'related to the frequency of the unit=oscillator 'in accordance 3 with the relationship l n-l- 1 as set forthabove, the count t2 producedat point b is directly proportional to interval-T2.

Upon the appearance of pulse P2, oscillator I9 produces a second series of pulses at point a. Simultaneously, -gate'46 is 4?. Gate 43 remains closed, however,-sinc no pulse appears at the input of'circuit 44. --Upon a second coincidence between'a pulse at point a and a pulse from the unit oscillator, as indicated in Fig. 6, a signal appears at the input of gated-6 I and passes throughgate 45 and circuit 44 to open gate 43. Gate 43 remains open until pulse P2 reaches the output of delay circuit 67, at which time pulse P2 passes through circuit 45 to-close gate 43. Thus, the number of pulsesof the sec- 0nd series appearing at point I), and recorded by counter @Lis representative of time interval ts.

Actually, under the assumption of the lower frequency for oscillator I!) stated above, the number of pulses of the second series occurring during the interval between pulse Pzand the'second coincidence is directly proportional-to time interval T4, where, in terms of unit intervals, 1T4=T3. In otherwords, in terms of fractional counts, t4=nt3. Accordingly, if delay circuit '41 delays pulse P2 for a period of time'equalto the time interval between n pulses from oscillatOr i 9, the count is of the second series recorded in counter AI will be directly proportional to interval T3. The total count of interval A t in the system of Fig. 5, in terms of unit intervals, is, therefore, equal to the count in of the unit counter plus the count t2+t3 of'counter ll divided by n. As in'theprevious embodimentsjthe time delay ofoscillator l9 will not eiTect the total fractional count, since any change in count izdue to the delay will produce an equal and opposite change in count t3, and since the totalfractional count is proportional to t2+ts.

It is apparent that the system ofFig.-'5 does not require the addition of one unit to the count recorded inthe unitcounter. The removal of this surplus unit count may be accomplished by delaying-the opening of the-gatecoupled to the unit counter for atime interval equal to onep'e- P2- isapplied to delay circuit ii i 1 0 riodof the unit pulse osc illator. "Anysuitable'di lay network may be employed for accomplishin the delay. In-this manner, the recorded un count will be :exactly equal to unit time ir terval T1.

In the-embodiments of the invention-thus fa 'describe'd, the fact that either-or' both of-pulse Pi-and- Pc may occur in'tirn proximity to one c the pulses from the unit -puls'e oscillator intro duces a -possibility-oferror in th recorded uni count. Thusfif pulse P1 occursclose to one o the unit pulses,-the initial unit pulse may b missed, or an additional unit pulse -may b counted. A similar situation may arise if puls P2 occurs close to one of the unit pulses. -Ai ambiguity is, therefore, introduced into the re corded unit count. Fig. 7 isa modification of th system of Pig. '2 .for removing this ambiguity witl re'spectto the-unit count.

Referring-now to Fig. 7 the fraction measuring section comprising-decoder iii-conductor I l, or circuit 3, fraction oscillator l9, pulse shaper '22 gates 23 and 25, and counter 2|and'24, is ridentical with and performs the same function as the fraction counting section of Fig. 2. Similarly, unit oscillator H, pulseshaper l3, coincidence circuit i5 and counter i2 are-identical with their counterparts in Fig.2. Pulse shaper I3 is connected tocounter l2 through a gate 5! and an or circuit 62.

The output of -coincidencecircuit 15, besides 'being'applied to'the closing control terminalsof eachof gates 23 and 25, as in the system of Fig.2, is applied to the input end of each opening control terminal ofwgatet i and to one input terminal of "or" circuit 65. The output terminal'of gate 64 is connected to its-closingcontrol terminal, to the closing control terminal of itsclosing control terminal. In-operation, referringto Fig. 8, the fractional intervals T2 and T3 are measured by means of counter 2| and 24, respectively, in amanner identical with that-of the system'of-Fig. 2. Thus, the pulses tzappearing at point (1, and recorded by counter 2i, are representative of the interval T2,

point e, and recordedby counter 24, are representative of the Whetherthe count of counter 2i In order to elimi-nate the-ambiguity as to the initial'count recorded in counter itythi's counter initially'cou-nts the pulses appearing at point e, the output of .pulse shaper- 22. This-operation is Jmplished by opening gate 61 with pulse P1, ;hat the pulses at point pass through gate and circuit 62 to point 1, the input end of nter I2. Gate 61 remains open until the first ncidence between a pulse at point e and a pulse point b, the output end of pulse shaper I3. this first coincidence, a signal appears at the put end of coincidence circuit I and is apad to gate 67, through gate 63 and circuit 65, close gate 61. In this manner, counter I2 ini- Ily counts the pulsesoccurring at point 0 durthe interval between pulse P1 and the first ncidence. at the first coincidence, the output signal from ncidence circuit I5 is applied to gate BI, rough gate 63, to open gate 6|. With gate BI an, the pulses appearing at point I) pass rough gate BI and circuit 62 to point 1, the int end of counter I2. Thus, counter I2 begins mting the unit pulses from point D and con- .1183 to count these pulses until a second coinlence occurs between a pulse at point I) and a .lse at point 0. Prior to the second coincidence, pulse P2 apars at the output end of decoder I6 and opens .tes 6A and B9 and triggers oscillator I9. With fee 69 open, the first pulse appearing at point passes through gate 69 and enters delay circuit Thus, when the second coincidence occurs, 1 indicated in Fig. 8, the output signal from Iincidence circuit I5 passes through gate 64 to cse gate BI, and passes through gate 64 and rcuit 86 to open gate 61. With gate BI closed, 1e pulses at point I) no longer reach point 1, hile with gate 61 open, the pulses at point 0 ass through gate 61 and circuit 62 to point f. 1 this manner, counter I2 stops counting unit ulses at the second coincidence and begins ounting the pulses appearing at point 0. Countr I2 continues to count the pulses appearing t point 0 until a fixed time interval after the ppearance of the first pulse at pointe, as deermined by delay circuit 68. After this fixed nterval, this first pulse appears at the output nd of circuit 68 and passes through circuit 65 0 close gate 61. It is thus seen that counter I2 nitially counts the first series of pulses at point 0 luring the time interval between pulse P1 and he first coincidence, intermediately counts the ,eries of pulses at point 1) during the time inter- 'al between the first and second coincidences, inally counts the second series of pulses at point a during the time interval between the second :oincidence and a, point a fixed time interval titer pulse P2. The delay introduced by circuit 53 is preferably equal to n times the-period of )scillator I9, so that counter I2 stops counting zhe pulses of the second series at the instant of arrival at point e of the nth pulse of the second series, as shown in Fig. 8.

In this manner, counter I2 switches to counting unit pulses only after the unit pulses have been definitely related in time to the pulses at point e, and, since the pulses at point 0 are started by pulse P1, the ambiguity as to the initial unit count is removed. Similarly, counter I2 stops counting unit pulses at the instant the unit pulses have been definitely related to the series of pulses started by pulse P2, and no ambiguity exists as to the final unit count. It is to be noted that the number of pulses initially counted by counter I2 is actually one less than the number of pulses appearing at point 12 during the time interval between pulse P1 and the first coincidence. However, since the number of time intervals is always one less than the number of pulses, the count recorded in counter I2 would be correct. Thus, in

determining the exact unit count, it becomes necessary to subtract n from the count recorded by counter I2, or preset counter I2 to -n before the time measurement is made.

It should be noted that, as in the previous embodiments, any variations in the time delay in actuating oscillator I9 will not efiect the total measurement of the fractional time intervals. Furthermore, since counter I2 measures the unit time interval by initially counting vernier pulses during the interval between pulse P1 and the first coincidence and finally counting vernier pulses during the interval between the second coincidence and the nth pulse of the secondseries of vernier pulses, any error introduced into the unit count, by time delay in initiating the first series of vernier pulses, will be compensated for by the equal and opposite error introduced into the final counting step by the delay.

It is clear that the unit counting system of Fig. 7 may be applied to the system of Fig. 4 as avell as to that of Fig. 2. In modifying the system of Fig. 4 in this manner, the fraction counting section would be the same, and the unit counting section would be identical with that of Fig. '7.

Referring now to Fig. 9, there is shown another embodiment of the present invention which includes both the non-ambiguous feature and the single fraction counter. In Fig. 9, unit oscillator II, unit counter I2, pulse shaper I3, decoder I6, or circuit I8, oscillator I9, pulse shaper 22 and coincidence circuit I5 are identical with their counterparts in Fig. 2. The output of pulse shaper I3 is applied to counter I2 through a gate 8| and an or circuit 82. The output of pulse shaper 22 is applied to a counter 83 through a gate 84.

The output terminal of coincidence circuit I5 is connected to the input terminals of a pair of gates 85 and 86,'the output terminals of gates 85 and 86 being connected to their respective closing control terminals. The output terminal of gate 85 is also connected to the opening control terminal of gate SI and to one input terminal of an or circuit 81. The output terminal of gate 86 is also connected to the closing control terminal of gate 8| and to one input terminal of an or circuit 88. Pulse P1 is applied to the opening control terminal of gate 85, and to the other input terminal of circuit 88. Pulse P2 is applied to the opening control terminal of gate 86, and to the input terminal of circuit 81 through a fixed delay circuit 89 similar to delay circuit 68 of Fig. '7. The output terminals of circuits B1 and 88 are applied to the closing and opening control terminals, respectively, of gate 84. The output of gate 84, in addition to being applied to counter 83, is applied to counter I2 through circuit 82.

In operation, referring to Fig. 10, unit oscillator II is continuously running and produces a first series of pulses at point I), the output end of pulse shaper I3. Prior to the time pulse P1 appears at point a, the input end of decoder I6, gates BI and 84 are closed and no pulses have been recorded in either counter I2 or counter 83. Upon the appearance of pulse P1, gates 84 and 85 are opened and oscillator I9 is triggered. Triggering of oscillator I9 produces a second series of pulses at point e which pass through gate 84 to point (1, the input end of counter 83. This second series of pulses also appears at point e, the input end semen -of counter i I2, -lb'y -passmgvthrough gate- 84 and I circuit 82.

At a first coincidencebetween a pulse -at point b and-a pulse at point:c,- a'signalappears in the output of coincidence circuit I5, and passes through open gate' 85'- to open gate B l. Thissignal also passes throughgatetiiand circuit8'l to close gate 84. Thus, the initial count tzrecorded in -'counte1' 83-is-representative of fractional time interval T2. Ifoscillator- I9 has a lowerfrequency 1. than that of oscillator l L as setforth in-connec- -tion with the'embodimentof -Fig; 4, the initial count 222 of counter 83 is directly proportional to interval T2.

With gate BI open-and gate' fliclosed, counter I2 stopscounting the'pulses of the second series and begins counting the pulses of-the. first series.

Counter 12 continues to count the-pulses of the first series untila second coincidence between "a pulse at point b andla' pulse at point e. Priorato the second coincidence pulsePz arrives andopens gate 86 and triggers oscillator I9. This-triggering of oscillator I9 produces a third series of pulses at point e, as indicated in Fig. 10. Upon the second coincidencethe vsigna1 appearing at the output end of coincidence circuit I 5-p-asses through gate ttandcloses gate-BI. Simultaneously; the signal at the outputendof coincidence circuit I5 passes through gate 86and circuit 88 to open gate 8 3. Thus, at the second'coincidence, counter I2 stops counting the pulses of the first I series and'begins counting the pulses of the third series. Furthermore, with'gate' 84 open, counter '83 also begins to countthe pulses of the third series.

. Each of counters I2 and83 :continues'tocount the pulses of the third series until pulse P2 reaches .the outputend oi Tdelay'circuit 89. As in the embodiments of Figs. 5 and 7, delay circuit 89 introduces a delay equalto the'time interval between n pulses from oscillator I9. Thus, as in the embodiment of "Fig. "5, the second -fractional count 153 recorded in 'counter'83' is proportional to interval T3, as shown in waveform'a in Fig. 10.

Furthermore, as in'the embodiment of Figf7, the total count t1+n recorded in counter I2 is equal to T1-+n. The total 'count of interval At, in terms of the unit count, is then equal to the count t1+n recorded in counter I2 minusn,

plus the count t2+tsrecorded in counter 83 divided by n.

It is thus seen that the presentinvention providesa methodand apparatus for measuringtime intervals, the method and apparatus providing a single Vernier orfraction oscillator for interpolating at each end of thetime interval to: be

measured. By utilizing a-single Vernier oscillator, the numberof required components is-reduced, and the necessity for additional frequency control is eliminated. has been described with particular reference to the measurement of the interval between pulses,

it is clear that the disclosed method and appa-' ratus may be applied to other signals. It is also clear that periodic signals other than pulses may wise than as specifically described.

What is claimed asnew is:

Although the invention I Apparatus for measuring the .time: interva between first and second signalsspaced from eacl othergsaid apparatus comprising a continuousl: running generator forgenerating a first series '0 periodic signals, a Vernier signal generator responsive to the first and second signals for gen erating a second and third series of periodi signals, respectively, the periods of said secom and third signals being-the'same, means couple! to said continuously running .generator for producing an indication of-thenumberbfsignal:

of s'aidfirst series occurring during the'time' i'n- 'te'r'val to be measuredgand counting means coupled to said Vernier signal generator forpro'd'ucing an indicationrepresentative of th'e time interval between thefirst signal-"and'the initiai signal ofsaid first-series occurring during the time intervalto be measured; and oithetiine interval between the second signal and thefina] signal of said first series occurring-during the time interval to bemeasured.

2. Apparatus according to claim l-whereinthe periods of said second and third series of signals are related to the period of saidfirstseries of signals in accordance with the relationship Where'n is an integer.

'3. Apparatus according to claim 1- wherein the periods of said second and third series of signals are related to the period of said first seriesof signals in accordance with the relationship where n is an integer.

4. Apparatusfor measuring the time interval between first'an'd second'signalsspaced from each other, sai'd apparatus com-prising a continuously running generator for generating a first series of uniformly spaced pulses,- a vernier'pulse genera-tor, means for triggering said Vernier pulse generator in-response to the'firstand secon'd pulses to-produce a second and third series of uniformly spaced pulses, respectively, the spacings between the pulses of said second and third series being equal and bearing a Vernier relationship to the spacing between the pulses of said Jfirst series, means coupled to said'cont'inuou'sly runninggenerator for counting the number of .pulses of saidfir'st series occurring during the time interval to be measured, and meanscoupled -to' said vernier pulse-generator for counting the number of pulses of said second series occurring during-the interval between the first pulseand coincidence between a pulse ofsaid first "series and a pulse of said second series, and for countingthe number of pulses of said thirdseries occurring during the interval between the second pulseand coincidence betweenapulse of said first series and a'pulse'of said-thirdseries.

5. Apparatus according to claim 4, wherein the last-named means comprises a single counter for producing a count equal to the (inference between the counts of the number of pulses'of said second and third'series.

6. Apparatus for measuring the time interval between first and second signals spaced frcnreach other,*--said apparatus comprising a continuously running generator for generating a "first series of uniformly spaced pulses,-avernier' pulse generator, means for triggering said Vernier pulse generatorinresponse to the firstand second pulses to' produce a second and third series of 15 .iformly spaced pulses, respectively, the spac- ;s between the pulses of said second and third :ies being equal and being related to the spacbetween the pulses of said first series in cordance with the relationship iere n is an integer, means coupled to said coniuously running generator for producing an dication of the number of pulses of said first ries occurring during the time interval to be easured, and means coupled to said vernier nerator for indicating the number of pulses said second series occurring during the time terval between the first pulse and coincidence :tween a pulse of said first series and a pulse said second series, and for indicating the numer of pulses of said third series occurring during le interval between coincidence between a pulse said first series and a pulse of said third series id the nth pulse of said third series.

7. Apparatus for measuring the time interval atween first and second pulses spaced from each ;her, said apparatus comprising a continuously H inning generator for generating a first series of niformly spaced pulses, a vernier pulse genera- )r, means for triggering said vernier pulse genrator in response to the first and second pulses produce a second and third series of uniformly paced pulses, respectively, the spacings between 1e pulses of said second and third series being qual, a unit pulse counter, means coupled beween said vernier pulse generator and said unit ulse counter for counting the number of pulses f said second series occurring during the time iterval between the first pulse and a first coacidence between a pulse of said first series and pulse of said second series, means coupled beween said continuously running generator and aid unit pulse counter for counting the number f pulses of said first series occurring during the ime interval between said first coincidence and second coincidence between a pulse of said first cries and a pulse of said third series, means oupled between said vernier pulse generator and aid unit pulse counter for counting the number at pulses of said third series occurring during he interval between said second coincidence and he nth pulse of said third series, where n is an nteger, and means coupled to said vernier pulse :enerator for counting the number of pulses of ;aid second series occurring during the interval )etween the first pulse and said first coincidence, ind for counting the number of pulses of said ;hird series occurring during the interval be- ;ween the second pulse and said second coin- :idence.

8. Apparatus for measuring the time interval Jetween first and second pulses spaced from each ither, said apparatus comprising a continuously running generator for generating a first series of miformly spaced pulses, a vernier pulse genera- ;or, means for triggering said vernier pulse generator in response to the first and second pulses to produce a second and third series of uniformly spaced pulses, respectively, the spacings between the pulses of said second and third series being equal, a unit pulse counter, means coupled between said vernier pulse generator and said unit pulse counter for counting the number of pulses of said second series occurring during the time interval between the first pulse and a first coincidence between a pulse of said first series and a pulse of said second series, means coupled between said continuously running generator and said unit pulse counter for counting the number of pulses of said first series occurring during the time interval between said first coincidence and a second coincidencebetween a pulse of said first series and a pulse of said third series, meanscoupled between said vernier pulse generator and said unit pulse counter for counting the number of pulses of said third series occurring during the interval between, said second coincidence and the nth pulse of said third series where n is an integer, a vernier .pulsecounter, and means coupled between said vernier pulse generator and said vernier pulse counter for producinga count in said vernier pulse counter of the number of pulses of said second series occurring during the interval between the first pulse and said first coincidence, and for producing a count in said vernier pulse counter of the number of pulses of said third series occurring during the interval between said second coincidence and the nth pulse of said third series.

9. Apparatus for measuring the time interval between first and second signals spaced from each other, said apparatus comprising a continuously running generator for generating a first series of periodic signals of a predetermined period, means coupled to said generator for producing an indication of the multiple number of said predetermined period occurring during the time interval to be measured, a single vernier signal generator for generating periodic signals of a period bearing a vernier relationship to said predetermined period, means for actuating said vernier signal generator in response to the first and second signals to produce a second and third series of periodic signals, respectively, and means coupled to said vernier signal generator for producing an indication of the fractional time interval remaining at each end of the time interval to be measuredv whenever the time interval to be measured is not exactly equal to a multiple number of said predetermined period.

10. Apparatus as defined in claim 9, wherein the last-named means includes first counting means coupled to said vernier signal generator for counting the number of signals generated by said vernier signal generator during the time interval between the first signal and a first coincidence between a signal from said continuously running generator and a signal from said vernier signal generator, and second counting means coupled to said vernier, signal generator for counting the number of signals generated by said vernier signal generator during the time interval between the second signal and a second coincidence between a signal from said continuously running generator and a signal from said vernier signal generator.

11. Apparatus as defined in claim 9, wherein the last-named means includes a single counter and means for coupling said counter to said vernier signal generator to produce an indication on said counter of the summation of the fractional time interval between the first signal and the initial signal of said first series occurring during the time interval to be measured and the fractional time interval between the second signal and the final signal of the first series occurring during the time interval to be measured.

12. The method of measuring the time interval between a first and second signal spaced from each other wherein a single vernier signal generator is employed to measure the fractional time interval remaining whenever the time interval to be measured is not equal to a multiple number of the period of a continuously rumiing signal generator, said method comprising the steps of producing a first indication representative of the number of signals of the continuously running generator occurring during the time interval to be measured, triggering the vernier signal generator by the first and second signals to produce a first and second series of periodic signals, respectively, producing a second indication representative of the fractional time interval between the first signal and the initial signal of the continuously running generator occurring during the time interval to be measured, and producing a third indication representative of the fractional time interval between the second signal and a final signal of the continuously running generator occurring during the time interval to be measured.

13. The method defined in claim 12 wherein the periods of said second and third series of signals are related to the period of the signals 18 of said continuous running generator in accordance with the relationship where n is an integer 14. The method defined in claim 12 wherein the periods of said second and third series of signals are related to the period of the signals of said continuous running generator in accordance with the relationship n+1 T where n is an integer.

WILLIAM E. FRADY, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,504,852 Lewis Apr. 18, 1950 2,560,124 Mofenson July 10, 1951 

